I've got a three column page where the center column overlaps the left one from about half way down. I don't have the same problem on any other pages on the site which use the same stylesheet. The strange thing is that once you refresh the page everything sits ok.
You have two elements with the ids main1 and also main2. Maybe the latter two are supposed to just have a class middle instead? That looks like it will set the margins closer to what you want...